Fabrication of interdigital delay lines



Sept. 7, 1965 R c. SIBLEY FABRICATION OF INTERDIGITAL DELAY LINES Filed July 10, 1961 INVENTOR Robe/'7 6. Sibley BY ATTORNEY United States Patent Office 3,Zfl5,l04 Patented Sept. 7, M365 3,205,104 FABRICATION F INTERDIGITAL DELAY LINES Robert C. Sibley, Wiliiamsport, Pa., assignor, by mesne assignments, to Litton Industries, Inc., Beverly Hills, Califi, a corporation of Delaware Filed July 10, 1961, Ser. No. 123,017 3 Claims. (61. 1566) The invention relates to the manufacture of an interdigital delay line such as is utilized in electrical traveling wave guides to retard the propagation of the waves along the guides.

In one form of such a delay line, the interdigital structure comprises a channel with the central section or web portion provided with flanges directed outwardly from the web. Also forming part of the delay line are spaced parallel fingers or bars fixed to one flange of the channel extending toward, but not reaching, the other flange, these bars being interdigitated with and spaced from like bars extending from the other flange of the channel. All of the bars or fingers are spaced from the web portion of the channel.

It is an object of this invention to simplify the construction of such a delay line whereby but a few steps are necessary to form a complete delay line.

It is a particular object to provide a method that Will insure accurate bar-to-bar spacing over the total length of the delay line.

Other objects will become apparent upon further consideration of the following description.

In brief, one embodiment of the invention is directed to a process of forming a delay line by providing a metal channel with its opposite flanges dentated to form teeth and by securing metal bars of uniform cross section to the flanges between the teeth thereof. Each of the bars, preferably, are tripartite with a long section of one metal having an end secured to one of the flanges between teeth thereof, a second, short intermediate section of another metal positioned close to the other of the flanges and a third short metal section within the said other flange. The bars are oriented so that the long sections are alternately secured in opposite flanges. Subsequently, the short intermediate sections of the bars which lie close to the flanges are removed.

By choice of suitable metals in the channel and particularly in the bars, the short intermediate sections may be removed by the application of means such as abrasion or etching techniques.

For a better understanding of the invention, attention is directed to the following description and accompanying drawings in which:

FIG. 1 is a perspective view of a fragment of a metal channel with teeth formed in the flanges into which bars are to be laid;

FIG. 2 is a perspective view of three adjacent metal bars showing their orientation with respect to one another;

FIG. 3 is a view of a fragmental portion of a channel with the bars set between the teeth of the flanges;

FIG. 4 is a perspective view of a fragmental portion of a delay line made in accordance with the invention; and

FIG. 5 is an end view of the delay line fragment shown in FIG. 4.

In accordance with one aspect of the invention, advantage is taken of the difference in susceptance to chemical reaction or in hardness of the metals utilized in the tripartite bars to obtain a clear line of cleavage and definite spacing between a finger and an adjacent flange.

Referring to FIG. 1, it is preferred, from the standpoint of rigidity, conductivity, and other factors, to make the waveguide channel 10 of tungsten or molybdenum. Channel 10 comprises a web 12 and flanges 14 and 16 into which teeth 18 have been cut as by milling them thereacross. Into an opposite pair of the teeth is brazed or otherwise secured the tripartite bar 24). Where the bar is to be separated by abrasion, the long end section 22 and the short end section 24 are formed of hard materials, while the intermediate section 26 is formed of a much softer material, and lies close to one flange of the channel. While not limited to the specific metals employed, a good example of acceptable metals is tungsten or molybdenum for the end sections 22 and 24 and iron or aluminum for the intermediate section 26. Tungsten is preferred for the end sections and iron for the intermediate section. These sections are all rigidly fixed to one another by brazing, welding, or the like. If desired, large slugs of tripartite bar material may be formed and then diced or cut to form individual bars. The next pair of teeth would be fitted with a bar 20 but with the ends 22 and 24 reversed so that the section 26 will lie adjacent the opposite flange 14. The third bar would be oriented like the first bar and succeeding bars alternated in the same fashion.

After all the bars have thus been secured in the slots between the teeth, an abrasive material such as sand or emery may be directed against the softer areas, and the iron or aluminum or the like is easily removed thereby. Since there is a distinct difference in hardness of the metals constituting the bar, a clean separation of metals takes place. The obtaining of such a clean separation is enhanced by utilizing a line stream of abrasive and utilizing a fine particle abrasive. The result is the formation of a delay line as shown fragmentarily in FIGS. 4 and 5. In this instance, after removal of section 26, the end of section 24 substantially forms a continuous surface with the channel flanges.

Another method of forming the delay line in accordance with the broad principles of the invention is to lay the tripartite bars, as before, in the slots of the flanges between the teeth and in alternation as to the position of the intermediate section, as heretofore described. However, instead of removing the intermediate portion 26 by abrasive action, said section is removed by acid etching thereof.

The choice of acid or acids and the strength thereof should, of course, depend upon the metals used. Where tungsten or molybdenum is utilized as the channel metal and as the end bar sections, the intermediate section may be of iron or aluminum, and the acid may be a dilute solution of hydrochloric acid. In this instance, tungsten is preferred as the channel metal as well as the metals of the end bar sections, with iron being preferred as the intermediate section. The hydrochloric acid may have approximately 10 percent strength, although other strengths may be used in accordance with the speed of reaction found desirable.

There is thus disclosed methods of manufacture of an interdigital delay line where after assembly of bars and channel, it is merely necessary to separate the tripartite bars at their areas where they are most susceptible to the action of an abrasive or of acid. Delay lines thereby produced have bar-to-bar spacings of desired accuracy in repetitive sequence.

Although several embodiments of the invention have been shown and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

Having thus described the invention, what is claimed is:

1. In a method of manufacturing an interdigital delay line, the steps comprising fixing tripartite metallic bars of uniform cross section into spaced slots in opposed parallel flanges of a metal channel and flush with the upper surfaces of the flanges and separating said bars from one of the flanges by removing one of the tripartite portions of each bar adjacent to a flange, the portions removed from the bars alternating so that they are adjacent opposite ends thereof, said method being further characterized by each of the bars being comprised of a long sections of a hard metal, an intermediate section of a soft metal and an end section of a hard metal, the bars alter nating with respect to the position of the soft section, and said separation of the bars being effected by abrading away the soft metal.

2. In the method of manufacturing an interdigital delay line, the steps comprising fixing tripartite bars of 25 bars alternating so that they are adjacent opposite ends thereof, said method being further characterized by each of said bars being comprised of a long section resistant to the action of a dilute acid, an intermediate section etchable by said acid and a third section having a characteristic similar to that of the first section, the channel also being resistant to the etching action of the dilute acid, the bars being positioned to alternate the positions of the acid etchable sections and to position said acid etchable sections adjacent to one of said flanges, said method further comprising applying a dilute acid to the bars to etch away the intermediate sections.

3. The method as set forth in claim 2, wherein the long section is of tungsten, the intermediate section is of iron and the third section is a short end section of tungsten.

References (Cited by the Examiner UNITED STATES PATENTS 2,501,164 3/50 Durst l566 X 2,827,588 3/58 Guenard et a1 33331 X 2,888,595 5/59 Warnecke et al. 33331 X FOREIGN PATENTS 620,228 5/61 Canada.

ALEXANDER VYMAN, Primary Examiner.

EARL M. BERGERT, JACOB STEINBERG, CARL F. KRAFFT, Examiners. 

1. IN A METHOD OF MANUFACTURING AN INTERDIGITAL DELAY LINE, THE STEPS COMPRISING FIXING TRIPARTITE METALLIC BARS OF UNIFORM CROSS SECTION INTO SPACED SLOTS IN OPPOSED PARALLEL FLANGES OF A METAL CHANNEL AND FLUSH WITH THE UPPER SURFACES OF THE FLANGES AND SEPARATING SAID BARS FROM ONE OF THE FLANGES BY REMOVING ONE OF THE TRIPARTITE PORTIONS OF EACH BAR ADJACENT TO A FLANGE, THE PORTIONS REMOVED FROM THE BARS ALTERNATING SO THAT THEY ARE ADJACENT OPPOSITE ENDS THEREOF, SAID METHOD BEING FURTHER CHARACTERIZED BY EACH OF THE BARS BEING COMPRISED OF A LONG SECTIONS OF A HARD METAL, AN INTERMEDIATE SECTION OF A SOFT METAL AND AN END SECTION OF A HARD METAL, THE BARS ALTERNATING WITH RESPECT TO THE POSITIONS OF THE SOFT SECTION, AND SAID SEPARATION OF THE BARS BEING EFFECTED BY ABRADING AWAY THE SOFT METAL. 